linux-kernel - Re: [PATCH v2] wait while adding MMC host to ensure root mounts

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Message-ID: <CAPDyKFp27MUOjhydLXf92vN3cua=XcX4oTJnMGfOJPpBhtwM8Q@mail.gmail.com>
Date:	Wed, 27 Mar 2013 12:13:12 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Chris Ball <cjb@...top.org>
Cc:	Sergey Yanovich <ynvich@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Namjae Jeon <linkinjeon@...il.com>,
	linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: Re: [PATCH v2] wait while adding MMC host to ensure root mounts

On 22 March 2013 18:03, Chris Ball <cjb@...top.org> wrote:
> Hi Sergey,
>
> On Wed, Mar 13 2013, Sergey Yanovich wrote:
>> MMC hosts are added asynchronously. We need to wait until detect returns to
>> avoid failed root filesystem mounts.
>> ---8<---
>> VFS: Cannot open root device "mmcblk0p1" or unknown-block(0,0): error -6
>> Please append a correct "root=" boot option; here are the available partitions:
>> mmc0: host does not support reading read-only switch. assuming write-enable.
>> 1f00             256 mtdblock0  (driver?)
>> 1f01             256 mtdblock1  (driver?)
>> 1f02            2560 mtdblock2 mmc0: new SDHC card at address b368
>>  (driver?)
>> 1f03           29696 mtdblock3  (driver?)
>> 1f04           16384 mtdblock4 mmcblk0: mmc0:b368 USD   3.72 GiB
>>  (driver?)
>>  mmcblk0: p1
>> b300         3910656 mmcblk0  driver: mmcblk
>>   b301         3906560 mmcblk0p1 00000000-01
>> Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
>> ---8<---
>>
>> Signed-off-by: Sergey Yanovich <ynvich@...il.com>
>> ---
>> changes for v2:
>> - removed exporting as symbol is in the same file
>>
>>  drivers/mmc/core/core.c |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>> index aaed768..7196888 100644
>> --- a/drivers/mmc/core/core.c
>> +++ b/drivers/mmc/core/core.c
>> @@ -2225,6 +2225,7 @@ void mmc_start_host(struct mmc_host *host)
>>       host->rescan_disable = 0;
>>       mmc_power_up(host);
>>       mmc_detect_change(host, 0);
>> +     mmc_flush_scheduled_work();
>>  }
>>
>>  void mmc_stop_host(struct mmc_host *host)
>
> Thanks, this looks okay to me, I've pushed it to mmc-next for 3.10.
>
> - Chris.
> --
> Chris Ball   <cjb@...top.org>   <http://printf.net/>
> One Laptop Per Child

Hi Chris,

I noticed you merged this. I thought the idea was to use the rootwait
or rootdelay?

Moreover, this patch will have bad impact on booting the kernel, since
every host device that has scheduled a detect work from it's probe
function will also wait for it to finish. Even if it is the boot
device of not. If this is needed, I would prefer that a host cap is
used.

Kind regards
Ulf Hansson
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